The present invention relates to a device for regulating the delivery pressure of a pump, e.g. for feeding fuel to an internal combustion engine.
In modern engine fuel feed systems, a low-pressure pump draws the fuel from a tank and feeds it to a high-pressure pump, which in turn feeds it to a distributor or so-called xe2x80x9ccommon railxe2x80x9d for supplying the engine cylinder injectors. To control and maintain a constant fuel pressure in the common rail, pressure-sensor-controlled devices are normally provided to drain any surplus fuel back into the tank.
Known pressure control devices normally comprise a solenoid valve in turn comprising a supply conduit communicating with the delivery conduit of the high-pressure pump, and a drain conduit communicating with the tank. The solenoid valve is also provided with a shutter located between the supply and drain conduits, and an electromagnet energized to control an armature controlling the shutter.
In one known pressure regulating solenoid valve, incorporated in a radial-piston pump, the electromagnet has a core with an annular solenoid; the armature is disk-shaped and fixed to a stem sliding inside a hole in the core coaxial with the solenoid; and the shutter is defined by a conical end of the stem, or by a ball controlled by the end of the stem.
Known regulating devices have several drawbacks. In particular, the fuel pressure in the delivery conduit is subject to various forms of disturbance, which impair operation of the engine, and which are caused, in particular, by the pulsating action of the high-pressure pump pistons, and by pulsating fuel delivery by the injectors.
Known devices are also subject to pressure disturbance caused by the piston effect of the armature stem, in turn caused by variations in fuel pressure when the supply conduit is opened. That is, upon the electromagnet opening the regulating solenoid valve, the delivery pressure acts immediately on the whole section of the stem, thus opening the solenoid valve instantaneously and causing the armature to vibrate.
The electromagnet is controlled by electric pulses having a given frequency, which, using the pulse width modulation (PWM) technique, also causes disturbance in the fuel pressure in the common rail; and, since the solenoid valve has a given resonance frequency, the resultant of the various forms of disturbance may, in certain conditions, generate resonance phenomena resulting in an enormous increase in disturbance.
It is an object of the present invention to provide an extremely straightforward, reliable device for regulating the delivery pressure of a pump, and which provides for eliminating the aforementioned drawbacks typically associated with known devices.
According to the present invention, there is provided a device for regulating the delivery pressure of a pump, e.g. for feeding fuel to an internal combustion engine, and comprising a solenoid valve in turn comprising a supply conduit communicating with the delivery of said pump, a drain conduit, a shutter between said supply conduit and said drain conduit, and an electromagnet energized variably to control an armature controlling said shutter; characterized by comprising reducing means for reducing disturbance in the delivery pressure of said pump.
More specifically, the reducing means comprise a cutoff chamber located between the supply conduit and the drain conduit, and of such a volume as to reduce the action of the variation in delivery pressure on the armature; and the armature comprises a cylindrical stem having a portion housed inside the cutoff chamber, and which is smaller in diameter than the stem, so as to increase the volume of the chamber.
In one embodiment of the invention, the cutoff chamber is closed by a fixed shield having an opening in which the smaller-diameter portion of the stem slides, so as to reduce the action of the fuel pressure on the stem.
If the electromagnet is controlled by an electronic unit comprising a pulse generator for generating pulses with a given frequency, and a pulse duty cycle modulator, the disturbance reducing means so condition the pulse generator as to generate a pulse frequency such as to avoid the resonance frequency of the solenoid valve.